Abrasive finishing tool having a rotary pneumatic motor

ABSTRACT

A pneumatic abrading or polishing tool is provided that includes a motor having a rotor, a motor housing, a carrier part having a shaft and a key extending from the shaft, and an abrading or polishing head attached to the carrier part. The motor housing contains a progressive exhaust passage including a preliminary portion that relieves at least some of the air pressure inside the motor before the exhaust passage fully opens.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 60/882,907, filed on Dec. 30, 2006 and entitled “IMPROVED ROTOR AND ROTOR HOUSING FOR A PNEUMATIC ABRADING OR POLISHING TOOL,” the entire content of which is hereby expressly incorporated by reference.

FIELD OF THE INVENTION

This invention relates generally to an improved motor housing for an abrading or polishing tool, such as an orbital abrading or polishing tool, and more particularly to such a motor housing having a progressive exhaust.

BACKGROUND

A known orbital abrading or polishing tool includes a motor having a rotor which rotates inside a motor housing. The rotor transmits a rotational force to a carrier part having an abrading or polishing head attached thereto. In this tool, a key extends from the carrier part and engages a keyway in the rotor, such that rotation of the rotor causes a corresponding rotation of the carrier part and the abrading or polishing head. The rotation of the rotor is caused by the introduction of compressed air through an inlet in the motor housing to one or more chambers formed between vanes in the rotor body. The compressed air flows through the inlet and contacts the rotor, causing it to rotate. As the rotor spins, the chambers progressively increase in size, permitting the compressed air to expand. The expanded air is then exhausted through one or more exhaust passages in the motor housing.

The exhaust passages of such tools are typically formed as abrupt openings in the motor housing. When the rotor spins to a position in which a particular one of the chambers overlaps the exhaust passages, the compressed air that was introduced into that chamber to rotate the rotor exhausts abruptly through these passages. This sudden release of air from the spinning motor can be very loud and distracting. Accordingly, a need exists for an improved motor housing for a rotary abrasive tool.

SUMMARY OF THE INVENTION

In accordance with the present invention, an abrasive finishing tool having a rotary pneumatic motor is provided. The motor includes a rotor that rotates inside a motor housing. Compressed air enters the motor housing through an inlet and causes the rotor to rotate. The motor housing contains a progressive exhaust passage including a preliminary portion that relieves at least some of the air pressure inside the motor before the exhaust passage fully opens. This progressive design can reduce the sudden noise caused by an abrupt exhaust opening.

In one embodiment of the present invention, an abrasive finishing tool having a rotary pneumatic motor is provided. The tool includes an abrading or polishing surface; a carrier part connected to the abrading surface; a stator having an inner surface defining a motor cavity; and a rotor contained within the motor cavity and engaging the carrier part in a driving relationship; the stator has an inlet opening for introducing an expandable fluid into the motor cavity, and further has a progressive exhaust channel having a preliminary portion that relieves at least some of the air pressure inside the motor cavity before the progressive exhaust channel fully opens.

In another embodiment of the present invention, an abrasive finishing tool having a rotary pneumatic motor includes a motor having a rotor and a housing containing the rotor; a carrier part engaging the rotor; and an abrading head attached to the carrier part; the housing comprising an inlet passage configured to introduce air into the motor and a progressive exhaust passage having a preliminary portion configured to release air from the motor prior to the release of air through a secondary portion greater in cross section than the preliminary portion. The preliminary portion of the progressive exhaust passage may comprise a preliminary slot, and the secondary portion of the progressive exhaust passage may comprise a secondary slot offset from the preliminary slot.

Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the features of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of an abrasive finishing tool according to an exemplary embodiment of the invention;

FIG. 2 is an enlarged central vertical cross-sectional view of the abrasive finishing tool of FIG. 1;

FIG. 3 is a horizontal cross-sectional view taken primarily on the line 3-3 of FIG. 2;

FIG. 4 is a fragmentary vertical cross-sectional view taken on the line 4-4 of FIG. 3;

FIG. 5 is an exploded perspective view of various components of an air motor of the abrasive finishing tool of FIG. 1;

FIG. 6 is an enlarged top plan view of a rotor according to an exemplary embodiment of the invention;

FIG. 7 is a front perspective view of a motor housing according to an exemplary embodiment of the invention;

FIG. 8 is a rear perspective view of the motor housing of FIG. 7;

FIG. 9 is a side elevational view of the motor housing of FIG. 7 rotated to show the full extent of its exhaust; and

FIG. 10 is a fragmentary perspective view of the motor housing of FIG. 7.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the drawings is intended as a description of the presently preferred embodiments of an abrasive finishing tool having a rotary pneumatic motor provided in accordance with the present invention and is not intended to represent the only forms in which the present invention may be constructed or utilized. It is to be understood that the same or equivalent functions and structures may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention. For example, whereas the pneumatic tools of the invention are described herein as using compressed air, in fact any suitable other compressed gas or expandable fluid can be used. As denoted elsewhere herein, like element numbers indicate like elements or features.

As shown in FIGS. 1-10, embodiments of the present invention are directed to a power abrading or polishing tool, such as a pneumatic orbital abrading or polishing tool, which includes a motor having a rotor that transmits a rotational force to a carrier part having an abrading or polishing head attached thereto. The rotor is contained in a motor housing which includes an inlet passage and one or more exhaust passages. Compressed air or other suitable gas enters the motor housing through the inlet passage and causes the rotor to rotate within the motor housing. As the rotor rotates, the gas expands and then exits through the exhaust passage. The exhaust passage has a progressive design including a preliminary portion that relieves at least some of the gas pressure inside the motor housing before the exhaust passage fully opens.

As shown in FIG. 1, the orbital tool 10 has a body structure 11 shaped externally as a handle to be grasped by a user for holding the tool and moving it along a typically horizontal work surface 12 to sand or polish that surface. In operating the tool, a user holds the tool by grasping the upper handle portion 26 and then pressing downwardly on a lever 107 to open a valve 83 and thereby admit compressed air or other suitable gas to the motor 13. Thus, air may be supplied to the motor cavity from a source 20 (shown schematically) of compressed air through a line 21 connecting into the rear of body structure 11.

As shown in FIGS. 3 and 4, the motor housing 35 includes an inlet passage 70 through which compressed air flows into the motor cavity 43, and exhaust passages or slots 302 and 304 through which air flows out of the cavity. Compressed air is delivered to the inlet passage 70 from the inlet line 21 through the manually actuable valve 83. The valve 83 is contained within a block 84 attached to the tool's rigid main body part 22.

When compressed air enters the motor cavity 43, it causes the rotor 42 of the motor 13 to rotate. The air driven motor 13 drives a carrier part 14 rotatively about a primary vertical axis 15. An orbitally driven part 16 is connected to the carrier part 14 for free rotation about a secondary vertical axis 17 displaced horizontally from the primary vertical axis 15. The part 16 carries an abrading or polishing head or shoe 18 and an abrasive or polishing sheet 19 as the part 16 moves orbitally about the axis 15 to sand or polish the surface 12. Thus, when the user grasps the tool 10 and presses down on the lever 107, the compressed air enters the motor cavity 43 and causes the rotor 42 to rotate, causing orbital motion of the abrading head 18.

The rotor 42 spins inside a stator or housing 35 of the motor 13. The housing 35 has a vertical inside wall 47 which may be cylindrical but eccentric with respect to the primary axis 15. Externally, the rotor 42 has a vertical cylindrical surface 66 centered about the axis 15 and therefore eccentric with respect to the inside wall 47 of the motor housing 35 as seen in FIG. 3. The rotor 42 has a plurality of vanes 67 which are free to slide radially within slots 68 of the rotor to engage the inside wall 47 of the housing 35 and to divide the space between the rotor 42 and the housing 35 into a plurality of chambers 69. The chambers 69 vary progressively in size as the rotor turns so that the introduction of air into these chambers through an inlet passage 70 in the side wall 36 of the motor housing 35 causes rotation of the rotor in a clockwise direction as viewed in FIG. 3, and hence a corresponding rotation of the carrier part 14 and the head 18. As the rotor 42 spins, the vanes 67 slide in and out of their individual slots 68 to remain in contact with the inside wall 47 and to thereby substantially seal the individual chambers 69 from each other.

Compressed air enters an individual chamber 69 through the inlet passage 70 and begins to expand inside that individual chamber 69. This expanding air causes the rotor 42 to rotate against the inside wall 47 of the housing 35. As the rotor rotates, the individual chamber 69 increases in size. The air expands and the rotor rotates until the chamber 69 overlaps the exhaust passages 302 and 304. The expanded air is then free to exit through these exhaust passages 302 and 304 and flow through outlet passages 86 in the body 22 and block 84. The outlet passages 86 lead to a vertical tube 87 in the block 84, and this tube 87 delivers the exhaust downwardly into an exhaust tube 88 leading to a discharge hose 89.

In the embodiment shown in FIGS. 7-10, the exhaust passages 302 and 304 are offset with respect to each other in the direction of rotation of the rotor 42 such that one of them “opens” relative to the chamber 69 before the other one does. This “opening” of the passages occurs as the vanes 67 move past the passages upon rotation of the rotor, providing exhaust paths for compressed air contained within the chambers. In addition, when the following vane 67 moves past the passage, the passage “closes” relative to the preceding chamber 69. Thus, the primary exhaust passage 302 opens before the secondary exhaust passage 304 opens. The portion P of the exhaust passage 302 is the preliminary portion of the exhaust, and the portion S of the exhaust passages 302 and 304 is the secondary portion of the exhaust. The preliminary portion P relieves at least some of the air pressure inside the chamber 69 before the exhaust passages fully open in the secondary portion S. This progressive exhaust thus allows some of the pressure inside the motor to be relieved before both passages are fully open.

When the compressed air enters an individual chamber 69 inside the motor cavity 43, it begins to expand and causes the rotor 42 to rotate in a clockwise direction. The rotor spins until the chamber 69 is aligned with the exhaust passages. The preliminary portion P is the first portion of the exhaust passage that the chamber reaches. The preliminary portion P of the primary exhaust passage 302 allows some of this air to escape and thus provides initial relief to the air pressure inside the cavity 43. The rotor continues to rotate, bringing the chamber 69 into open alignment with the secondary portion S, where both exhaust passages are open. This secondary portion S has a larger cross sectional area than the preliminary portion P and provides the greatest area for exhausting the air from the chamber 69. As the rotor continues to rotate along the inside wall 47 of the housing 35, the chamber 69 moves past the secondary portion S. The rotor then begins another rotation cycle around the motor cavity 43.

Because the two passages 302 and 304 are offset, the preliminary portion P provides preliminary pressure relief without abruptly opening both exhaust passages to their full volume. In the embodiment, shown, the preliminary portion P has a smaller cross-sectional area than that of the secondary portion S. This progressive design provides a more gradual opening of the exhaust passage. Because the air inside the chamber 69 begins to leak out through the preliminary portion P before fully exhausting through both passages 302 and 304 in the secondary portion S, the exhaust process is more gradual than an abrupt opening of both passages at the same point. This progressive opening can help to reduce the loud noise caused by an abrupt exhaust.

In the embodiment shown in FIG. 9, the slot 302 overlaps the slot 304. The first slot 302 opens before the second slot 304 opens, and closes after the second slot 304 has opened but before the second slot 304 has closed.

As shown in FIGS. 7-10, the primary and secondary passages 302 and 304 are formed in the side wall 36 of the motor housing 35. The motor housing 35 also includes a first recess 308 formed in the outside surface of the housing approximately opposite the passages. The housing also includes a second recess 306 that encompasses at least a part of the length of the two passages 302 and 304. This second recess 306 provides a receiving space for the air exiting the motor cavity 43. Air flows into this recessed space and then into the outlet passage 86 in the body 22 and further to the discharge hose 89.

Even within the preliminary portion P, the exhaust passage may have a progressive design where the air first flows down the primary passage 302 toward the recess 306, as shown in FIGS. 8 and 10. The initial portion I of the primary exhaust passage 302 opens before the recess 306 begins. When the air inside the chamber 69 reaches this initial portion I, the air has to flow down the length of this initial portion I before it reaches the recess 306. This opening provides some initial pressure relief before the primary passage 302 fully opens into the recess 306. As the chamber 69 moves further around the cavity 43, it reaches the next portion of the passage 302 that extends into the recess 306. The air can exhaust through this portion of the passage 302 directly into the recess. As the chamber 69 continues to rotate around the cavity, it reaches the secondary portion S, where both exhaust passages are fully open.

This progressive exhaust is further shown in FIG. 10, where the vane 67 and the chamber 69 are rotating clockwise through the motor cavity. When the vane 67 is in the first position shown in the figure, the chamber 69 is aligned with the initial portion I of the primary exhaust passage 302. Air A is shown flowing through the initial portion I toward the recess 306. When the vane 67 moves into the second position, the chamber 69 is aligned with the preliminary portion P. The air inside the chamber can exit directly into the recess 306. The vane 67 continues to move into alignment with the secondary portion S, where both passages 302 and 304 are open. The two offset passages shown in FIGS. 7-10 are one embodiment of the progressive exhaust feature, but this feature is not limited to two offset passages and may be designed in other ways. As will be readily apparent to those skilled in the art, other progressive exhaust designs may also be used, such as, for example, a slot or passage that widens or expands in the direction of rotation of the rotor 42.

As shown in FIGS. 2 and 5, the housing 35 includes a vertically extending side wall 36, a top wall portion 37 carrying a bearing 38, and a bottom wall 39 carrying a second bearing 40. A horizontal circular plate 41 is located above the bottom wall 39. The rotor 42 of the motor is contained and driven rotatively within the motor cavity 43 formed by the housing parts. The housing 35 may be made of any durable material, such as steel or other ferrous material. The housing 35 also includes a key 312 (shown in FIG. 7) which engages the rigid body 22 to prevent relative rotation or movement between the housing 35 and the body 22.

As shown in FIG. 3, the side wall 36 of the motor housing has an external cylindrical surface 46 which fits closely within and engages the internal cylindrical surface 23 of the rigid main body part 22. Internally, the side wall 36 has a vertical surface 47 which may be cylindrical but eccentric with respect to axis 15, and more particularly may be centered about a vertical axis 48 which is parallel to but offset from the axis 15 to give the desired eccentricity to the surface 47. As shown in FIGS. 2 and 5, the top wall portion 37 has a planar horizontal undersurface 49 forming the top of cavity 43 within which the rotor 42 is received. The top wall portion 37 has an outer edge surface 50 which is received closely adjacent the internal surface 23 of the part 22. At its upper side, the top wall portion 37 has an annular surface 51 which is engaged by the annular flange 25 of the body part 22 to clamp the top wall portion 37 downwardly against the side wall 36 of the motor housing 35. Radially inwardly of the surface 51, the top wall portion 37 has an annular portion 52 defining a cylindrical recess 53 within which the outer race of the ball bearing 38 is received and located. The externally cylindrical vertical shaft portion 44 of the carrier 14 is a close fit within the inner race of the bearing 38, and is retained against downward withdrawal from the bearing 38 by a washer 54 secured to the shaft 44 by a screw 55 connected into the upper end of the shaft. The washer projects radially outwardly far enough to engage the upper surface of the inner race of the bearing 38 to maintain the parts in assembled condition.

The bottom wall 39 of the motor housing or stator is similar to the top wall portion 37, but inverted with respect to the top wall. More particularly, the bottom wall 39 has an upper planar horizontal surface 56, a cylindrical outer edge surface 57 which fits fairly closely within the cylindrical surface 23 of the body part 22, and a horizontal annular undersurface 58 which is engaged annularly by the shoulder surface 31 of the retainer 29 to clamp the bottom wall 39 upwardly against the side wall 36 of the motor housing 35. Radially inwardly of the surface 58, the bottom wall 39 has a downwardly projecting annular portion 60 defining an essentially cylindrical recess 61 within which the bottom ball bearing assembly 40 is received and located. The inner race of the bearing 40 is a close fit about the externally cylindrical shaft portion 44 of the carrier 14, to contact with the upper bearing 38 in the mounting part 14 for its desired rotation about the axis 15. The top wall portion 37, bottom wall 39, and motor housing 35 form the motor cavity 43 within which the rotor 42 spins. As shown in FIG. 5, the rotor 42 is connected to an upper shaft portion 44 of the carrier 14, to drive that carrier rotatively about axis 15. The rotor 42 has an inner cylindrical passage 62 that fits closely about the external cylindrical surface 63 of the shaft portion 44 of the carrier part 14. A key 64 received within opposed axially extending grooves in parts 44 and 42 transmits rotary motion from the rotor 42 to the shaft 44. A leaf spring 65 interposed radially between the rotor and key may exert radial force in opposite directions against these parts to take up any slight looseness which may occur.

As shown in FIGS. 5 and 6, the rotor 42 includes a generally cylindrically-shaped outer body 120 that surrounds a central core 122. The outer body 120 is composed of a first material and the core 122 is composed of a second material having a greater resistance to wear than the first material. In one embodiment, the core 122 may be made of or comprise a suitable metallic material, such as steel or a composite containing metallic powder, and has a high resistance to wear. The outer body 120 may then be made of or comprise aluminum or other light metallic alloys or compositions, or any suitable polymeric material having sufficient strength and durability to withstand the rotational forces and wear to which the rotor 42 is subjected. The outer body 120 may also be moldable to form an integral body with the core 122. Materials for the outer body 120 include a variety of olefins, phenolics, acetals, polyamides (including 612 nylon or carbon fiber filled 46 nylon), or other suitable resinous materials. In a particular embodiment, a synthetic material used for the outer body 120 may be reinforced by any fibrous material suitable for use in a bearing structure. Such fibrous materials may include, for example, glass fiber, carbon fiber, or synthetic fibers such as aramid.

As shown in FIGS. 5 and 6, the radial slots 68, which receive the vanes 67 (described above), are disposed in the outer body 120 of the rotor 42, and the inner cylindrical passage 62 forms a through passage in the core 122. The inner cylindrical passage 62 includes a keyway 124 that receives the key 64 of the shaft 44 of the carrier part 14. Preferably, the core 122 of the rotor 42 is non-rotatably coupled to the outer body 120 of the rotor 42, such that when compressed air flows against the vanes 67 causing a rotation of the outer body 120 of the rotor 42 (described below), the core 122 correspondingly rotates, which in turn causes a rotation of the carrier part 14 via the interaction of the keyway 124 of the core 122 and the key 64 of the shaft 44 of the carrier part 14.

In one embodiment, as shown in FIG. 6, in order to prevent a relative rotation between the outer body 120 and the core 122, an inner surface of the outer body 120 includes an alternating series of protrusions 130 and recesses 132, and the outer surface of the core 122 includes a corresponding alternating series of protrusions 136 and recesses 134. Each protrusion 130 on the inner surface of the outer body 120 mates with a corresponding one of the recesses 134 in the outer surface of the core 122, and each protrusion 136 on the outer surface of the core 122 mates with a corresponding one of the recesses 132 in the inner surface of the outer body 120. This causes the core 122 and the outer body 120 to interlock securely with one another to prevent rotation between them. In one embodiment, the rotor 42 is formed by molding, casting or otherwise forming the outer body 120 onto the core 122. One such process is the injection molding of the outer body 120 onto the core 122. In such processes, the core 122 becomes an integral component with the outer body 120.

In one embodiment, as shown in FIG. 6, each radial slot 68 is aligned with and extends into a corresponding one of the protrusions 130 on the inner surface of the outer body 120. This maximizes the depth D to which each radial slot 68 may extend. In addition, in this embodiment, each protrusion 136 on the outer surface of the core 122 extends between adjacent ones of the radial slots 68. This arrangement reduces the likelihood of the rotor 42 fracturing in use at one of the radial slots 68. Because the known non-metallic rotor (described above) does not include the described reinforcing metal core 122 of greater wear resistance, the radial slots in the known rotor cannot be made to the same depth as those of the present rotor 42 without risk of fracture. This is significant because the stability of a vane is directly related to the proportion of the vane contained within the slot.

In one embodiment, the outside diameter (OD) of the rotor 42 is approximately 1.35 inches, the depth (D) of each radial slot 68 is approximately 0.415 inches, and the width (W) of each radial slot 68 is approximately 0.070 inches. As such, each radial slot 68 is formed to a depth that is approximately 30% of the outer diameter (OD) of the rotor 42.

As is also shown in FIG. 6, a cavity 140 may be disposed between each radial slot 68 and adjacent to each protrusion 136 on the outer surface of the core 122. These cavities 140 extend into the rotor 42 from both its upper surface and its lower surface (see FIG. 2), terminating in a central web adjacent the core 122. As such, the cavities 140 reduce the overall mass of the rotor 42 without adversely affecting its torsional stability. Because the rotor 42 has the core 122 with protrusions 136, the rotor 42 is light but extremely durable. The use of a metallic core avoids wear at the keyway 124, and the protrusions 136 permanently lock the polymeric outer body 120 of the rotor 42 to the core 122 of the rotor 42. The disclosed rotor 42 is therefore able to operate in its intended manner indefinitely.

As described above, a key 64 extends from the carrier part 14 and engages the keyway 124 in the rotor such that rotation of the rotor causes a corresponding rotation of the carrier part 14 and the abrading or polishing head 18. Beneath the level of the lower bearing 40, the carrier part 14 has an enlarged portion 89′ which is typically externally cylindrical about the axis 15. The enlarged portion 89′ then contains a recess 90 centered about the second axis 17 which is parallel to but offset laterally from the axis 15. The orbitally driven part 16 has an upper reduced diameter portion 91 projecting upwardly into the recess 90 and is centered about the axis 17 and journaled by two bearings 92 and 93 for rotation about the axis 17 relative to the carrier 14, so that as the carrier turns the part 16 is given an orbital motion. The rotation of the lower enlarged portion 89′ of carrier 14 causes orbital movement of the head 18 and its carried sandpaper sheet 19, to abrade the work surface 12.

A lower enlarged diameter flange portion 94 of the part 16 has an annular horizontal undersurface 95 disposed transversely of the axis 17. A threaded bore 96 extends upwardly into the part 16 and is centered about the vertical axis 17, for engagement with an externally threaded screw 97 which detachably secures the head 18 to the rest of the device. A counterweight plate 98 may be located vertically between the carrier 14 and the flange 94 of the part 16, and be secured rigidly to the part 14 by appropriate fasteners. It may be externally non-circular about the axis 15 to counterbalance the eccentrically mounted part 16, the head 18, and any other connected elements.

The carrier part 14 carries the part 16 and the abrading head 18. The head 18 may be rectangular in horizontal section, including an upper horizontally rectangular rigid flat metal backing plate 99 having a rectangular resiliently deformable cushion 100 at its underside, typically formed of foam rubber or the like. The sheet of sandpaper 19 extends along the undersurface of the cushion 100, and then extends upwardly at opposite ends of the head for retention of its ends by two clips 101. The screw 97 extends upwardly through an opening in the plate 99 to secure the head 19 to the orbitally moving part 16. In other embodiments, the head 18 and sandpaper 19 may have other cross-sections, such as a circular cross-section.

As shown in FIGS. 2 and 4, the body structure 11 of the tool 10 may be formed as an assembly of parts including a rigid main body part 22 having an internal surface 23 defining a recess within which the motor 13 is received. The part 22 may be metallic and may have an outer surface 24 of square horizontal section and an annular horizontal flange 25 at its upper end for confining the motor against upward removal from the body. A square cushioning element 26 may be carried about the body part 22 and extend across its upper side, and may be formed of an appropriate rubber, to function as a cushioned handle element by which the device is held in use. A rigid reinforcing element 27 is bonded to the undersurface of the top horizontal portion of the handle cushion 26, and with the attached part 26 is secured to the body 22 by four screws 28 (see FIG. 4) extending downwardly through vertically aligned openings or passages in the parts 22 and 27, with the heads of the screws engaging downwardly against the part 27, and with the lower ends of the screws being connected threadedly to a retainer 29 which is tightenable upwardly against the motor to retain it in the recess 30 formed within the body structure. The radially inner portion of the retainer 29 forms an upwardly facing annular horizontal shoulder surface 31 (see FIG. 4) which projects radially inwardly beyond the surface 23 to block downward withdrawal of the motor. The lower portion of the retainer 29 forms a tubular circular skirt 32 to which the upper end of a tubular rubber boot 33 is secured by an annular clamp 34.

The lower end 102 of the flexible tubular boot 33 carries and is permanently attached to a plate 103 preferably formed of sheet metal which is essentially rigid. Plate 103 has a horizontal circular portion 104 extending parallel to the upper surface of plate 99, and at its periphery has an upwardly turned cylindrical side wall portion 105 fitting closely about and bonded annularly to the lower externally cylindrical portion 102 of rubber boot 33. The plate 103 has a central opening 106 through which the screw 96 extends upwardly, so that upon tightening of the screw the plate 103 is rigidly clamped between the plate 99 and the element 16, with the boot 33 then functioning to retain the head 18 against rotation relative to the upper portion of the tool.

The head 18 rotates against the work surface 12 to polish or sand the surface. In operation, the user presses down on the lever 107 to open the valve 83 and introduce compressed air into the individual chambers 69 inside the motor cavity 43. The air expands and causes the rotor 42 and chambers 69 to rotate, bringing them into alignment with the exhaust passages 302 and 304. The progressive design of the exhaust gradually relieves the air pressure and helps to reduce the loud noise associated with a sudden and abrupt exhaust of air.

Although the drawings illustrate the invention as applied to a pneumatic orbital sander, it will be apparent that the novel aspects of the air motor arrangement of the invention may also be utilized in other types of portable pneumatic abrading or polishing tools. The preceding description has been presented with reference to various embodiments of the invention. Persons skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structures and methods of operation can be practiced without meaningfully departing from the principles, spirit and scope of this invention. 

1. An abrasive finishing tool having a rotary pneumatic motor comprising: a motor having a rotor and a housing containing the rotor; a carrier part engaging the rotor; and an abrading head attached to the carrier part, wherein the housing comprises an inlet passage configured to introduce air into the motor and a progressive exhaust passage having a preliminary portion configured to release air from the motor prior to the release of air through a secondary portion greater in cross section than the preliminary portion.
 2. The abrasive finishing tool of claim 1, wherein the preliminary portion of the progressive exhaust passage comprises a preliminary slot and the secondary portion of the progressive exhaust passage comprises a secondary slot offset from the preliminary slot.
 3. The abrasive finishing tool of claim 2 wherein the preliminary slot overlaps the secondary slot.
 4. The abrasive finishing tool of claim 2 wherein the preliminary slot opens before the secondary slot opens and closes after the secondary slot opens.
 5. The abrasive finishing tool of claim 1, wherein the housing further comprises a recess formed in an outer surface of the housing and encompassing at least a portion of the progressive exhaust passage.
 6. The abrasive finishing tool of claim 1, wherein the rotor comprises a keyway that mates with a key on the carrier part to engage the rotor with the carrier part.
 7. The abrasive finishing tool of claim 1, wherein the housing is made of steel.
 8. The abrasive finishing tool of claim 1, wherein the tool is a pneumatic orbital abrading or polishing tool.
 9. The abrasive finishing tool of claim 1, wherein the rotor comprises an outer body and a central core.
 10. The abrasive finishing tool of claim 9, wherein the outer body and central core comprise mating protrusions that lock the outer body to the central core to prevent relative rotation therebetween.
 11. The abrasive finishing tool of claim 9, wherein the central core comprises steel.
 12. The abrasive finishing tool of claim 1, wherein the preliminary portion comprises a first portion of a first slot and the secondary portion comprises a second slot and a second portion of the first slot, such that the preliminary portion has a cross-sectional area that is less than the cross-sectional area of the secondary portion.
 13. An abrasive finishing tool having a rotary pneumatic motor comprising: an abrading or polishing surface; a carrier part connected to the abrading or polishing surface; a stator having an inner surface defining a motor cavity; and a rotor contained within the motor cavity and engaging the carrier part in a driving relationship, the stator comprising an inlet opening for introducing an expandable fluid into the motor cavity, and further comprising a progressive exhaust channel having a preliminary portion that releases at least some of the fluid inside the motor cavity before the progressive exhaust channel fully opens.
 14. The abrasive finishing tool of claim 13, wherein the progressive exhaust channel has a secondary portion configured to fully open the progressive exhaust channel, and wherein the preliminary portion has a cross-sectional area that is less than a cross-sectional area of the secondary portion.
 15. The abrasive finishing tool of claim 13, wherein the progressive exhaust channel comprises a plurality of offset slots.
 16. The abrasive finishing tool of claim 13, wherein the stator further comprises a recess formed in an outer surface of the stator and overlapping with at least a portion of the progressive exhaust channel.
 17. The abrasive finishing tool of claim 13, wherein the preliminary portion comprises a preliminary slot and the progressive exhaust channel comprises a secondary slot offset from the preliminary slot.
 18. The abrasive finishing tool of claim 13, wherein the rotor comprises an outer body surrounding a central core having a keyway that engages a key on the carrier part.
 19. An abrasive finishing tool having a rotary pneumatic motor comprising: a motor comprising a rotor configured to rotate inside a motor housing; a carrier part engaged with the rotor; an abrasive surface attached to the carrier part; the motor housing comprising an inlet and a progressive exhaust, and the progressive exhaust comprising a preliminary portion and a secondary portion, the preliminary portion being configured to release air from the motor before the secondary portion opens.
 20. The abrasive finishing tool of claim 19 wherein the preliminary portion is smaller in cross section than the secondary portion. 